The present invention relates to optical transducer systems, and is more particularly concerned with optical transducer systems of the kind involving an optical transducer which produces a wavelength multiplexed output signal, such as the transducer described in our United Kingdom Patent Application No. 8720156 (Publication No. 2 209 101A).
A wavelength multiplexed optical position transducer is described in our aforementioned United Kingdom patent application No. This transducer uses a graded-index rod lens and a glass wedge grating assembly to disperse and recombine a broad spectrum optical signal generated by an LED. The dispersed light is reflected by a coded strip and the combination of wavelengths present in the recombined spectrum is a function of the position of the lens/grating assembly relative to the coded strip.
The recombined signal from a transducer is transmitted along a single optical fibre to a detector system. The detector system wavelength demultiplexes the received signal in a further wedge/grating assembly.
Typically a ten bit coded strip is used in the transducer to reflect the various wavelengths in the dispersed optical signal. A further channel is sued to provide a continuous ON signal for use as a reference channel. This reference channel is used to compensate for wavelength-independent variable system losses such as poor optical connections, bent fibres, and ageing of the LED's. However, there may be further, wavelength-dependent, variations in intensity caused by factors such as temperature variations of the LEDs. The LEDs could have their temperatures stabilized by using PELTIER coolers but this is not a practical solution in many applications due to the low lifetime of Peltier coolers at elevated temperatures (e.g. 10,000 hours at 125.degree. C.).
Another drawback with the prior detector system is the fact that eleven data channels have to be dealt with simultaneously. This means that each channel requires a separate photodiode, pre-amplifier and phase-sensitive detector, which makes it difficult to reduce the size and weight of the detector system for applications such as aerospace, where these are important factors.
It is an object of the present invention to alleviate at least some of the drawbacks of the prior optical transducer and its detector system.